This study was initiated to understand the merozoite and erythrocyte factors in the eventual interiorization of the merozoite within the erythrocyte. The research at present is to determine: (1) the receptor system on erythrocytes for initiating invasion of Plasmodium knowlesi, P. vivax and P. falciparum; (2) the role of erythrocyte metabolism in parasite invasion and development; and (3) the merozoite structure in the surface coat that attaches to the receptors.